This invention relates generally to chemical mechanical polishing systems and processes.
Integrated circuits are typically formed on substrates, particularly silicon wafers, by the sequential deposition of conductive, semiconductive or insulative layers. After a layer is deposited, a photoresist coating is applied on top of the layer. A photolithographic apparatus, which operates by focusing a light image on the coating, is used to remove predetermined portions of the coating, leaving the photoresist coating on areas where circuitry features are to be formed. The substrate is then etched to remove the uncoated portions of the layer, leaving the desired circuitry features.
As a series of layers are sequentially deposited and etched, the outer or uppermost surface of the substrate, becomes increasingly non-planar. This non-planar surface presents problems in the photolithographic steps of the integrated circuit fabrication process. Specifically, the photolithographic apparatus may not be able to focus the light image on the photoresist layer if the maximum height difference between the peaks and valleys of the non-planar surface exceeds the depth of focus of the apparatus. Therefore, there is a need to periodically planarize the substrate surface.
Chemical mechanical polishing (CMP) is one accepted method of planarization. Chemical mechanical polishing typically requires mechanically abrading the substrate in a slurry that contains a chemically reactive agent. During polishing, the substrate is typically held against a rotating polishing pad by a carrier head. The carrier head may also rotate and move the substrate relative to the polishing pad. As a result of the motion between the carrier head and the polishing pad, abrasives, which may either be embedded in the polishing pad or contained in the polishing slurry, planarize the non-planar substrate surface by abrading the surface.
The polishing process generates vibrations that may reduce the quality of the planarization or damage the polishing apparatus.
In general, one aspect of the invention relates to a carrier head for chemical mechanical polishing. The carrier head has a base, a support structure attached to the base, and a retaining structure attached to the base. The support structure has a surface for contacting a substrate while the retaining structure prevents the substrate from moving along the surface. The retaining structure and the surface define a cavity for receiving the substrate. The retaining structure includes an upper portion in contact with the base, a lower portion, and a vibration damper separating the upper portion and the lower portion. The vibration damper includes a material that does not rebound to its original shape when subjected to a deformation.
In general, a second aspect of the invention relates to a chemical mechanical polishing apparatus that includes a polishing pad to polish a substrate and the carrier ahead described above.
Implementations of the first and second aspects of the invention may include one or more of the following features. The lower portion of the retaining structure may be thicker than the substrate to prevent the vibration damper and the upper portion from contacting the substrate. The lower portion of the retaining structure may define the walls of the cavity for receiving the substrate, and the vibration damper may reduce the transmission of vibration energy from the substrate through the lower portion to the upper portion. The lower portion may contact a polishing pad during polishing, while the vibration damper may reduce the transmission of vibration energy from the polishing pad through the lower portion to the upper portion. The retaining structure may be an annular wall around a periphery of the surface, and the vibration damper may be an annular ring separating the annular upper portion from the annular lower portion. The vibration damper may be mounted on the first portion and the second portion using a pressure sensitive adhesive. The lower portion may include a wearable member for contacting the polishing pad, and a support member may be mounted on the wearable member to add rigidity to the wearable member. The vibration damper may be mounted on the support member.
In general, a third aspect of the invention relates to a polishing station that includes a platen, a vibration damper mounted on the platen, and a substrate polishing pad mounted on the vibration damper. The vibration damper includes a material that does not rebound to its original shape when subjected to a deformation.
In general, a fourth aspect of the invention relates to a chemical mechanical polishing apparatus including the polishing station described above and a carrier head to press a substrate on the polishing pad when the substrate is being polished.
Implementations of the third and fourth aspect of the invention may include one or more of the following features. The vibration damper may be substantially disc shaped and may be mounted on the platen and the substrate polishing pad using a pressure sensitive adhesive. The polishing station may include a protective layer for mounting the polishing pad on the vibration damper. The protective layer may include a Teflon sheet, aluminum, or stainless steel, and the protective layer may be adhered to the vibration damper and the polishing pad using a pressure sensitive adhesive.
In general, a fifth aspect of the invention relates to a carrier head for positioning a substrate on a polishing surface. The carrier head includes a structure having a surface for contacting a substrate, a housing connectable to a drive shaft to rotate with the drive shaft about a rotation axis, and a gimbal mechanism between the structure and the housing to preventing the structure from moving out of the rotation axis. The gimbal mechanism prevents the structure from moving laterally while permitting the structure to gimbal relative to the housing. The gimbal has a top coupled to the housing, a bottom coupled to the structure, and a vibration damper separating the top from the bottom. The vibration damper includes a material that does not rebound to its original shape when subjected to a deformation.
In general, a sixth aspect of the invention relates to a chemical mechanical polishing apparatus that includes a polishing pad and the carrier head just described above.
Implementations of the fifth and sixth aspect of the invention may include one or more of the following features. The vibration damper may be mounted to the top and the bottom using a pressure sensitive adhesive. The housing may define a bushing, and the top may include a gimbal rod that extends into the bushing to couple the top to the housing, and a gimbal ring that is coupled to the gimbal rod. The bushing may allows the gimbal rod to move along the rotation axis while preventing the gimbal rod from moving out of the rotation axis. The vibration damper may be mounted on the gimbal ring using a pressure sensitive adhesive. The gimbal mechanism may include a substantially planar flexure ring that flexes in a direction perpendicular to the plane of the flexure ring to gimbal the structure to the housing. The damping material may be mounted on the flexure ring using a pressure sensitive adhesive.
Implementations of all the general aspects of the invention may include one or more of the following features. The damping material may rebound by less than ten percent of the deformation, preferably less than six percent of the deformation. The damping material may include a soft plastic or a visco-elastomer, such as an isodamp C-1000 series isolation damping material (e.g. C-1002 material).
The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.